In the field of subsea wells, the requirement of pressure ranges of the well assemblies is continuously increasing. This leads to corresponding increased technical requirements of the seal assemblies employed in such wells.
Metal-to-metal seals have been used for a long time with various designs. One of the challenges of such seals is that the metal used in the seal may experience tension beyond the yield strength of the material in the seal. Thus, when a pressure is removed the seal may have altered its shape, and may not be able to function properly with the next or a later exposure of high pressure. Hence, one wants to use a sealing member which shape is not permanently altered after exposure to a high pressure.
Further, a standard or prerequisite is that the metal in a sealing member, such as a sealing ring, is softer than the metal in the facing sealing surface. In other words, the metal in the part being easily substituted should be softer than the metal in the other. Also, this metal should be sufficiently soft to make it yield in the position of contact against the facing sealing surface, in order to provide for a tight seal.
Thus, these two objects are to some extent in contradiction to each other.
Patent application GB 2 217 795 exhibits a V-shaped seal element with a cross section showing two sealing legs. The two legs can be forced against an opposite facing sealing surface by two secondary legs which can be forced in a wedging manner between the said sealing legs.
U.S. Pat. No. 5,044,672 describes another metal-to-metal seal with a circular seal element having a cross section with two legs which form a V-shape.
Each leg exhibits a sealing surface which is forced against opposite sealing surfaces of elements of a subsea well assembly.
U.S. Pat. No. 5,174,376 also describes a seal assembly with a metallic seal element having a U-shaped cross section.
Furthermore, patent publication U.S. Pat. No. 7,559,366 yet another embodiment of a metal-to-metal seal. Here, an H-shaped sealing ring (or alternatively, to V-shapes arranged against each other) is forced against facing sealing surfaces by a wedging member which is forced into the space between the legs of the seal ring. In addition, the description mentions the possibility to arrange a layer of a softer metal on the side of the seal ring, in order to seal possible scratches or rifts in the facing sealing surface.
U.S. Pat. No. 6,367,558 B1 describes a metal seal with a cross section that exhibits two legs. A band of a softer metal than the metal of the rest of the seal is attached to the outside of the legs, for contact against an opposite sealing surface.
As briefly mentioned above, with continuously increasing pressure rates, the seals must be designed correspondingly. Both the need for a “soft” metal of the sealing member, with respect to the facing sealing surface, as well as the need for a sealing member which shape does not become permanently altered, must be met.